High Precision Imaging Method Utilizing Calibration and Apodization in Multibeam Imaging Sonar

Multibeam imaging sonar is widely used for underwater target detection and localization, and to obtain the high precision sonar image is especially critical in practical application. Among others, high sidelobes and amplitude and phase errors are the major challenges for such applications, due to array nonuniformity and imperfect channels. To overcome this deficiency, the high precision imaging method utilizing calibration and apodization in multibeam imaging sonar is proposed. In order to suppress the sidelobes, the magnitude and phase errors must be calibrated prior to the beamforming operation. Least squares estimation is applied to achieve the phase calibration, which is to search the minimum value between the measured phase difference and geometric phase difference in the near field of the array. After the magnitude and phase errors is calibrated, the nonlinear sidelobe apodization is applied to suppress the multibeam sidelobe. The proposed method is discussed using measured sector-scan imaging sonar data with frequency 200kHz in water tank. The tested results demonstrate that the proposed method results in the sonar image not only with lower sidelobes reaching a large dynamic range of above 40 dB but also with narrower mainlobe width equal to uniform weigting function.